Suzaku observation of two ultraluminous X-ray sources in NGC1313

Tsunefumi Mizuno, Ryohei Miyawaki, Ken Ebisawa, Aya Kubota, Masao Miyamoto, Lisa Winter, Yoshihiro Ueda, Naoki Isobe, Kazuo Makishima

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1 Citation (Scopus)


We report about the Suzaku observation of two ultraluminous X-ray sources (ULXs), X-1 and X-2, in NGC1313, together with their spectra by XMM-Newton. During the observation, both showed intensity-correlated spectral changes. The brighter source, X-1, exhibited the highest luminosity (∼3 × 10 40erg s-1) ever recorded from this source. Its spectral variation is ascribed to a strong power-law like component with a mild high energy curvature, while about 10% of the flux is carried by a stable soft component modeled by a cool disk emission. These properties suggest that the source was in the "very high" state, wherein the disk emission is strongly Comptonized and the optically-thick disk is truncated at a large radii or cooled off. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor disk model with the innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source gets brighter. Hence X-2 is interpreted to be in a slim disk state. These results suggest that the two ULXs host black holes of a few tens to a few hundreds solar masses.

Original languageEnglish
Pages (from-to)229-233
Number of pages5
JournalProgress of Theoretical Physics Supplement
Issue number169
Publication statusPublished - 2007
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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